Implantable medical devices include, among other things, cardiac rhythm management (CRM) devices such as pacers, cardioverters, defibrillators, cardiac resynchronization therapy (CRT) devices, as well as combination devices that provide more than one of these therapy modalities to a subject. External electrocardiograph (ECG) devices include, among other things, programmers (for programming implantable medical devices), recorders, monitors, or any other device capable of acquiring external ECG signals, such as by using external surface ECG electrodes attached to a patient's skin. Such externally acquired ECG signals typically include information about pacing pulses being delivered to the patient to evoke heart contractions. However, external ECG devices typically cannot independently distinguish between pacing pulses being delivered at different heart locations.